Extension for a heating duct



FIG. 1 is a perspective view showing my new design for an extension for a heating duct;

FIG. 2 is a left side elevation view which is a mirror image of the right side elevation view;

FIG. 3 is a bottom plan view;

FIG. 4 is a front elevation view which is a mirror image of the rear elevation view; and,

FIG. 5 is a top plan view. 

The ornamental design for an extension for a heating duct, as shown and described. 